It's pretty cheap and easy to add rear speakers to that mix and a nice subwoofer for those action movies.
It's pretty trivial to get set up. You buy an inexpensive surround sound receiver from Costco, buy your front and rear speakers, and a subwoofer and you're good to go. The investment here is probably $2K at most. Half of a Saturday afternoon will do it. The speakers don't even have to be expensive to enjoy it. Listening to the surround sound movie tracks doesn't require anything more than adequate speakers.
Heck, the receivers include a microphone to ping the room for you and set themselves up appropriately.